1. Field of the Invention
The present invention relates to a photoelectric conversion device and a camera including the same.
2. Description of the Related Art
A CCD- or CMOS-type photoelectric conversion device has been used in many digital still cameras and digital camcorders. In particular, a CMOS-type photoelectric conversion device has the advantage over a CCD-type one in terms of power consumption and multifunctionality, and its application range has recently widened.
A photoelectric conversion device uses a method for improving sensitivity by forming, as an antireflection film, an insulating film with an intermediate refractive index between the refractive indices of a photoelectric converter for converting light into an electric signal and an insulating film arranged thereon.
With an increase in number of pixels, the size of a pixel is smaller. This creates a need to reduce the size of a photoelectric converter in a photoelectric conversion region, and that of a MOS transistor in a photoelectric conversion region or peripheral circuit region. When an element becomes smaller, a margin in layout design also becomes smaller. If, therefore, the alignment accuracy of a contact hole for a diffusion region or gate electrode is low, penetration of an element isolation region may occur during etching for forming the contact hole. In this case, in operation of the photoelectric conversion device, an electric current may flow between a diffusion region in contact with a contact plug and a well in contact with the diffusion region.
To solve the above problem, a so-called self-aligned contact technique is well known. This technique prevents penetration of an element isolation region upon opening a contact hole by forming an insulating film having an etching stopper function capable of obtaining a selectivity ratio when forming, by etching, the contact hole for forming a contact plug. This technique is applied to a CMOS-type photoelectric conversion device with a small pixel size which requires a fine contact hole.
In a photoelectric conversion device disclosed in Japanese Patent Laid-Open No. 2004-228425, an etching stopper film is formed on a photoelectric converter in addition to an antireflection film. In this arrangement, the antireflection film and etching stopper film are stacked on a gate electrode for controlling transfer of charges accumulated in the photoelectric converter. This increases the thickness of a layer structure on the photoelectric converter, thereby decreasing the sensitivity and F-number proportionality.